Posted:
Feb 5, 2018 @ 6:06 am

An avalanche warning is in effect for the West central Montana backcountry.  The current avalanche danger is HIGH.  Very dangerous avalanche conditions exist.  Travel in and around avalanche terrain is not recommended. Large human triggered avalanches are likely.

This is Logan King with an avalanche warning for Monday, February 5th, 2017.  This avalanche warning is valid for 24 hours. The avalanche warning will either be extended or terminated at 0600 on February 6th.

This danger rating does not apply to operating ski areas and is the sole responsibility of the U.S. Forest Service.

 Weather and Snowpack

Snow and rain continue to impact the region. SWE’s across the area range from .9-1.6 inches of water this morning and an additional 6-12 inches of snow have fallen over the past 24 hours. Temperatures this morning at the majority of mountain locations are above 32 degrees and did not drop below freezing overnight. Rain line is currently around 5,500-6,000 feet, and rain was reported to over 7,000 feet yesterday. Ridge top winds are 22 mph gusting to 36 mph from the WNW.

A large and heavy load of snow has been added to the northern portion of the advisory area. We received reports of up to 2 feet of new snow yesterday, strong winds and dense snow falling. Further south heavy snow and rain have about 6,000 feet have added a significant load of water that is stressing the snowpack. Continued precipitation with the potential of up to another inch of water today are further complicating avalanche conditions.

With the snow/water totals we have seen, rain to unseasonably high elevations and strong winds; avalanche conditions have significantly deteriorated. Storm slabs, wet slabs, wind slabs, persistent and deep persistent avalanches are all possibilities today. With the multitude of problems and high probability of failures today, traveling around or on avalanche terrain is not recommended.

Keep in mind that the majority of avalanche accidents happen during or immediately after a storm. The snow pack doesn’t like rapid changes and has gotten a significant load over a short period of time. Conditions will remain touchy for the next couple of days until the snow has time to settle.

Ski and ride safe.

READ FULL ADVISORY  

Problem 1 - Storm Slabs

  • TYPE

    storm-slabs

    Storm Slabs

    Release of a soft cohesive layer (a slab) of new snow which breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

  • SIZE

    5-6

    2-3 (Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-6

    Likely/Very Likely

    The likelihood of an avalanche resulting from this problem.

A wet heavy load of snow has been added to the snowpack and will be touchy for a few days.

Problem 2 - Persistent Slabs

  • TYPE

    persistent-slabs

    Persistent Slabs

    Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks.  Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Persistent, Deep-Slab.

  • SIZE

    8-9

    4 (Very Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-5

    Likely

    The likelihood of an avalanche resulting from this problem.

Buried surface hoar is now deeply buried but is still reactive under the new load. The crusts higher up in the snowpack will provide bed surfaces for storm snow to move on especially in areas that are getting rain.

Problem 3 - Wind Slabs

  • TYPE

    wind-slabs

    Wind Slabs

    Release of a cohesive layer of snow (a slab) formed by the wind.  Wind typically erodes snow from the upwind sides of terrain features and deposits snow on the downwind side.  Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

  • SIZE

    6-7

    3 (Large-Very Large)

    The potential size of avalanche resulting from this problem.

  • LIKELIHOOD

    Likelihood-5

    Likely

    The likelihood of an avalanche resulting from this problem.

Strong winds with the storm have created touchy conditions near ridge tops and mountain passes.

FORECAST & OUTLOOK

A complex system is currently impacting the area. A frontal boundary has set up right across the advisory area. The northern region will see continued strong winds and snow today. The southern portion of the advisory area will see heavy wet precipitation with rain lines around 6,000 feet again today and have the potential for another inch of SWE to be added to the snowpack. Additional weather and forecast information can be found here.

This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.